Rotational carpet bevellers are commercially available. For example, National Carpet Equipment, Inc. of Minneapolis, Minn. manufactures bevellers used in the carpet industry. Carpet bevellers are typically used to remove pile from carpet edges. When pieces of bevelled carpet are placed adjacent one another, this bevelling can produce visually pleasing textural effects due to different light reflectivity at the “troughs” of abutted bevelled pieces. Depending on factors such as the texture of the carpet or ambient lighting, such effects may not always be apparent.
Rotational carpet bevellers often include a rotating cutter and a stationary, opposed, counter-knife, these two parts defining blades that co-operate to cut the pile of the carpet. The rotating cutter has a cutting edge that is formed to meet the counter-knife at an angle so as to produce a shearing action along the blades. The edge of the cutter is formed to sweep out a body of revolution, with the edge of the cutter then lying on the body of revolution so defined. By way of example, for a circular cylindrical body of revolution, the cutting edge may trace out a portion of a helix.
When adjacent one another, the cutting edge and counter-knife appear to form a closed, or acute, angle. As the cutter rotates, its cutting edge passes the counter-knife. When the counter-knife is viewed in plan view, an end of the rotating cutting edge first passes a corresponding end of counter-knife. As the cutter further rotates, the remaining end of the cutting edge passes the remaining end of the counter-knife. Cutting takes place at the point at which the cutting edge passes the counter-knife. If the cutting edge is partially along the surface of an imaginary cylinder, as in the form of a helix, then the cutting point moves from one end of the counter-knife to the other as the cutting edge passes the counter-knife. This moving point traces what is called a cutting line. The cutting line is often substantially parallel to the axis of rotation of the cutter.
Any carpet pile placed between the edges of the cutting edge and counter-knife is cut in a shearing action along the cutting line as the cutting edge passes the counter-knife. In a typical prior installation, the carpet pile is cut in a generally downward motion starting at the free ends of the pile, and moving towards the carpet base.
Rotational carpet bevellers typically have an axis of rotation (and cutting line) that forms an angle, either a right angle or an acute angle, with the surface of the carpet piece to be bevelled. A cutting area of the beveller is exposed to engage an edge of a carpet piece. The beveller is usually stationary with respect to the carpet piece. The carpet piece, lying substantially in the horizontal plane, is positioned relative to the cutting area so that, when the carpet piece is moved horizontally past the cutting area, the edge of the carpet piece encounters the cutting line and is bevelled at the angle of the straight cutting line.
The carpet edge is guided relative to the cutting area by a fence. The fence may be an adjustable guidance bar, which maintains the carpet edge at a desired distance from the cutting line as the carpet edge is moved horizontally past the cutting line along the fence.
The cutting line can be tilted through various angles to engage more or less of the pile element. The cutting line can be viewed as the hypotenuse of the right angled triangular section of pile which is removed. This right angle is formed by the pre-bevelled, vertical tuft row at the carpet edge and the horizontal plane of the carpet surface.
Conventional rotational bevellers have a straight cutting line and therefore transpose a straight-angled cut to a carpet edge. Even a single straight edge may not be well made by conventional bevellers because of the need for a clean vertical edge at the base of the carpet as will be described below. A pillow effect where there is a convex arc or rounded edge to the carpet can be achieved by multiple straight edged bevellers in line, or by multiple passes through the same beveller where there have been adjustments of the tilt axis or angle of the cutting line in co-operation with distance positioning of the carpet edge via the fence. Of course any number of straight edged bevellers in line could not achieve a concave edge.
It is desirable, but not essential, that a bevelled carpet edge exhibits the following features:
i) Clean Edge for Precision Abutment of Like Pieces:
It is generally desirable to create a clean bevelled carpet edge for precision abutment of like carpet pieces. Carpet pile is preferably oriented generally at right angles to the base of the carpet. Since carpet tuft elements are flexible, they sometimes lean from a vertical orientation. This is particularly true of rolled carpets. To bevel a carpet piece when there are leaning tufts, the edge of the carpet piece is preferably pre-cut using a cutting line angle that is substantially perpendicular to the plane of the carpet base. This pre-cut is not necessarily intended to bevel the carpet edge. It is intended to remove the ends of leaning tufts to make a clean carpet edge in preparation for bevelling.
If the carpet is bevelled before cleaning the carpet edge, leaning tufts are not generally removed effectively. When like carpet pieces are abutted, the leaning tufts can make a buffer zone (see next heading) look uneven. Leaning tufts may also make it difficult to cause adjacent carpet pieces to abut one another. Using a two-step bevelling operation, the edge is first cleaned in a cleaning pass of the carpet edge, and in a second step, the carpet is bevelled.
ii) Vertical Tuft Buffer Zone of Abutted Carpet Pieces
The bevel portion of a carpet piece is typically cut so that there is a small remaining vertical tuft element along the edge of the carpet piece. When like carpet pieces are abutted, this vertical element at abutting carpet edges forms a buffer zone which is intended to mesh sufficiently with adjacent buffer zones to mask the discontinuity of assembled carpet pieces. Without this vertical element, abutting carpet pieces can appear to be separate elements, rather than a visually pleasing single carpet, having a bevelled design.
To achieve an adequate buffer zone at the carpet edge, the fence is adjusted to encourage upper portions of the cutting line to intersect upper portions of pile element, while lower potions of the cutting line are distanced from the base of the carpet to leave lower portions of the pile element remaining to form the buffer zone. While this succeeds in leaving a sufficient vertical length of tuft element at the edge of the carpet piece, unless the carpet piece has been first run through a vertical cutter, the remaining tuft elements are often left leaning, frayed or unevenly cut. This occurs because after cutting, some of the tuft elements also extend beyond the cutting line, leaving a somewhat uneven edge. This uneven edge can lead to a visually displeasing buffer zone. Without this vertical element, abutting carpet pieces can appear to be separate elements, rather in a visually pleasing single-carpet having a bevelled design.
iii) Stylized Edge Design
It is often desirable to have pile removal at carpet edges to cause visual effects caused by different light reflectivity at the “troughs” of abutted bevelled carpet pieces. The ability to create different light effects is in part limited by the angle of the cutting line relative to the carpet base. A straight edge beveller can change the bevelled look by changing the angle of the beveller, however, there are advantages to creating a more rounded or “pillowed” bevelled look.
Attempts have been made to “pillow” the carpet edge. Pillowing is rounded or radiused edges rather than the straight bevel lines described above. Pillowing is generally achieved by mounting in series five or more bevellers with each beveller set at a slightly different cutting angle to define a section of a polygon. The multiple bevellers thus co-operate to produce a visually radiused carpet edge in the shape of the polygon section. Each side of the polygon is cut by a respective beveller, and each side is preferably short enough that the combined cut sides appear to form a generally rounded or “pillowed” edge. The pillowed edge can be difficult to achieve because all the bevellers must be precisely angled and positioned, and the carpet must be guided precisely past the blades of all of the bevellers. In addition, multiple bevellers must be used to create just one edge, which can increase equipment and maintenance costs.
Accordingly, there is a need for alternative bevellers for carpets.